1. Field of the Invention
Present invention relates to improvements to a metal gasket used as a joint seal interfacing three separate components in the form of a cylinder block, a chain case and a cylinder head of an internal combustion engine.
2. Description of the Prior Art
In a chain driving engine E, an independently manufactured chain case 2 is a neighboring component of and tightly connected to a cylinder block 1, as shown by FIGS. 19 and 20. There exists in this area three pairs of opposing surface areas, that is between the chain case and the cylinder block, and between an underside of cylinder head 3 and the chain case 2 whereat is provided a metal gasket A. It is this three opposing surface area region whereat a seal function is to be performed. B is a metal gasket provided between the cylinder block and the chain case. The A-B line shows a contacting boundary between the cylinder block 1 and the chain case 2.
In the independently manufactured structures, namely, the chain case 2 and the cylinder block 1, a slight height differential h exists caused by thermal expansion differences between the cylinder block 1 and the chain case 2 as shown by FIG. 21.
The occurrence of the above-mentioned height differential h leads to a diminished effectiveness of the seal function. On this account, an edge of an opening 4 for the chain in the metal gasket A is provided with an elastic seal member 5 (FIGS. 23 and 24) having a semicircular cross sectional view adjacent the mentioned height differential h. A paste or like liquid gasket material 6 is provided to ensure good sealing characteristics applied thereat.
However, when the fasteners securing the cylinder head and the chain case and/or cylinder block together are overtightened, then liquid gasket material is squeezed out of the joint due to overtightening pressure and the rubber-like elastomer is degradated. As a result, cracking occurs, or a sealing characteristic is diminished due to a decreasing of the rubber elasticity. Thus, engine oil leakage occurs where the cracking exists. The elasticity of the rubber, set before the metal gasket becomes further compressed when overtightening occurs, brings about a discrepancy because the elasticity of the rubber has been lost.
A metal gasket for sealing a region whereat there exists three sets of opposing pairs of surfaces between a cylinder block, a chain case and a cylinder head of a chain driving engine. The metal gasket includes an elastic seal member provided on an inner rim of a chain opening formed in said metal gasket, and a storing structure for liquid gasket material used for sealing. The storing structure is defined by an enlargement of the chain opening oriented to coincide with a juncture of the region whereat three pairs of opposing surface areas exist, the enlargement defining a cavity in which is housed liquid gasket material and a through hole is provided externally of the cavity.